1. Field of the Invention
This invention relates to a write head of optical printer, and more particularly to a write head of optical printer utilizing the principle of a vacuum fluorescent display device.
2. Description of the Prior Art
Optical printers utilizing various kinds of write heads have been proposed. The optical printer is generally constructed in such a manner as shown in FIG. 1. More specifically, the printer includes a photosensitive drum 1, and an electrifier 2, a write head 3, a developing device 4, an erasing lamp 5 and a cleaning blade 6 arranged around the photosensitive drum 1 in order in the clock-wise direction. A decalcomania paper 8 fed from a cassette 7 is moved linearly while being contacted with the drum 1 which is rotated in the direction indicated by the arrow or the clockwise direction. Reference numeral 9 designates a decalcomania or transferring heater.
Conventionally, an LED (light-emitting diode), an LCD (liquid crystal display) or the like is generally used as a write head in the optical printer. However, the LED is disadvantageous in that it fails to exhibit sufficient luminance at a wavelength suitable for writing operation, whereas the LCD is slow in shuttering operation for intermitting a rear light source in response to applied voltage. Accordingly, it is unable for these write heads to be operated by a dynamic drive, but operated by a static drive as shown in FIG. 2. The write head of the static driving type comprises a picture cell array 10 disposed on a substrate. The picture cell array 10 includes light emitting picture cells A, such as, for example, an LED or an LCD, linearly arranged together with a rear light source and is provided with a wiring 11 in each of the light emitting picture cells A.
As explained hereinabove, the write head of the static driving type is provided with the wiring 11 independently every light emitting picture A which is outwardly led out from the picture cell A. As a result, the number of the wirings 11 led out from the picture cell A becomes too numerous, and each of the wirings must be connected independently at the exterior of the write head when it is used for an optical printer which includes light emitting picture cells arranged at intervals as small as about 0.1 mm. As a result, the connection of the respective wirings is extremely troublesome and complicated, because a space required for leading out the wirings is insufficient due to the structural limitation of the write head.
In order to eliminate the above problem, a write head of optical printer as shown in FIG. 3 has been proposed which utilizes the principle of a vacuum fluorescent display device and employs a dynamic driving system. More particularly, the write head shown in FIG. 3 includes a picture cell array 10 which comprises light emitting picture cells A each comprising a phosphor layer deposited on an anode and arranged on a straight line having an interval therebetween and is divided into a plurality of groups 12a, 12b, 12c - - -. The corresponding picture cells A in each of the groups 12 are connected together by a common wiring, and grids G1, G2, G3 - - - are arranged above the light emitting picture cells A of the respective groups 12 so as to correspond thereto.
In the write head of the dynamic driving type described above, the corresponding light emitting picture cells in each of the groups are connected together by a common wiring. Thus, the problems inherent in the write head of the static driving type are effectively eliminated. However, the grid G is provided in each group 12 and it must be electrically separated from one another defining a grid gap S between the each adjacent two grids G and between the light emitting picture cells A. Accordingly, in the write head shown in FIG. 3, it is highly difficult to ensure an area necessary to form the grid gap S between the adjacent light emitting picture cells which are arranged at micro-intervals. Furthermore, the grid gap S and the interval between the picture cells prevent light emitted from the picture cells from forming together a full line along the direction of arrangement of the picture cells when the light is projected on a photosensitive drum. As a result, lines or characters formed of dots are printed on a decalcomania paper.